A patch antenna is a narrowband wide-beam antenna fabricated by etching the antenna element pattern in metal trace bonded to an insulating dielectric substrate, such as a printed circuit board (PCB), with a continuous metal layer bonded to the opposite side of the substrate which forms a ground plane. Common microstrip antenna shapes are square, rectangular, circular and elliptical, but any continuous shape is possible. Some patch antennas do not use a dielectric substrate and instead, are made of a metal patch mounted above a ground plane using dielectric spacers. The resulting structure is less rugged but has a greater bandwidth. Because such antennas have a very low profile, are mechanically rugged and can be shaped to conform to the curving skin of a vehicle, they are often mounted on the exterior of aircraft and spacecraft, or are incorporated into mobile radio communications devices.
Microstrip antennas are relatively inexpensive to manufacture and design because of the simple 2-dimensional physical geometry. They are usually employed at ultra-high frequencies (UHF) and higher frequencies because the size of the antenna is directly tied to the wavelength at the resonant frequency. A single patch antenna provides a maximum directive gain of around 6-9 dBi. It is relatively easy to print an array of patches on a large (single) substrate using lithographic techniques. Patch arrays can provide much higher gains than a single patch with little additional cost. Matching and phase adjustment can be performed with printed microstrip feed structures, again in the same operations that form the radiating patches. The ability to create high gain arrays in a low profile antenna is one reason that patch arrays are common on airplanes and other military applications.
Patch antennas are commonly used in a number of applications such as telecommunications and radar systems. A patch antenna may have a ground plane and a metallic patch of a predetermined shape disposed parallel to the ground plane. A dielectric may separate the patch from the ground plane. The region between the patch and the ground plane may create a resonant cavity that allows for the radiation of electromagnetic waves.
A patch antenna fashioned in this manner may be easy to manufacture and may have end use advantages compared to other antenna configurations. For example, the ground plane shields the antenna from interference from surrounding lines and electronics, and the antenna may be easily conformed to a surface. The frequency characteristics of a patch antenna are a function of the patch antenna size and geometry, which are generally fixed when the patch antenna is manufactured and the environment into which the manufactured patch antenna is introduced. Many patch antennas may be limited to a single frequency with a narrow bandwidth of only a few percent of the center frequency. It may be difficult to expand the bandwidth of the patch antenna or to operate the patch antenna at multiple frequencies. Moreover, the frequency characteristics of the patch antenna may be changed based on the operating environment or if the patch is damaged.
U.S. Patent Application Publication No. US 2010/0194663 A1 to Rothwell et al. entitled “Variable Frequency Patch Antenna” describes a patch antenna system which comprises a patch antenna having a patch spatially separated from a ground plane. A plurality of pins are interposed between the patch and the ground plane to selectively interconnect the patch to the ground plane. A control module is coupled to the plurality of pins and is operable to set an operating frequency characteristic of the patch antenna by selectively connecting the patch to the ground plane with one or more of the plurality of pins.
U.S. Pat. No. 7,385,557 B2 to Kim entitled “PIFA Device for Providing Optimized Frequency Characteristics in a Multi-Frequency Environment and Method for Controlling the Same” describes a planar inverted-F antenna (PIFA) device and a method for controlling the PIFA device that can provide optimized frequency characteristics in a multi-frequency environment. The PIFA device is provided with a plurality of shorting pins located at different distances from a feeding pin and an antenna switch capable of selecting one of the shorting pins, or is provided with an antenna switch capable of moving a shorting pin to a preset position, thereby adjusting a distance between the feeding and shorting points. Antenna frequency characteristics can be optimized according to a frequency band used at a current location, and the antenna frequency characteristics can be optimally maintained is a multi-frequency environment at any time.
U.S. Pat. No. 6,175,723 B1 to Rothwell, III entitled “Self-Structuring Antenna System with a Switchable Antenna Array and an Optimizing Controller” describes an antenna array defined by a plurality of antenna elements that are selectively electrically connectable to each other by a series of switches, so as to alter the physical shape of the antenna array. The antenna elements include antenna wires, where the wires of adjacent antenna elements are connected by a mechanical or solid state switch. One or more feed points are electrically connected to predetermined locations within the antenna array. A feedback signal from the receiver provides an indication of signal reception and antenna performance. The feedback signal is applied to a computer that selectively opens and closes the switches. An algorithm is used to program the computer so that the opening and closing of the switches attempts to achieve antenna optimization and performance.
U.S. Patent Application Publication No. US 2011/0175791 to Ozdemir et al. entitled “Multi-Beam, Polarization Diversity Narrow-Band Cognitive Antenna” describes a multi-beam, polarization diversity, narrow-band cognitive antenna system. The antenna system includes a plurality of antenna elements, switching elements, and transmission feed lines disposed on a printed circuit board (PCB) substrate, inside or on the enclosure of a consumer wireless device, on the airframe of an air vehicle, or on the surface of a ground vehicle. The plurality of switching elements are arranged with the antenna elements and transmission feed lines to, when selectively closed, electrically couple selected ones of the antenna elements and transmission feed lines to one another to generate an antenna configuration selected from a plurality of antenna configurations. A non-volatile memory is configured to store data representing at least some of the plurality of antenna configurations. A control arrangement is operatively coupled to the plurality of switching elements and configured to selectively close selected ones of the switching elements as a function of the data stored in the memory. Means are provided to selectively update the data as a function of previously selected antenna configurations.